In a generator rotor according to 3,131,321, each of the two feeding conductors, connected to the rotor winding, has a portion disposed parallel to the axial center line of the rotor and adjacent thereto, which portion is arranged in direct electrical connection with a first radially directed portion, which is located in a radially directed bore. From this radial portion, the electric connection continues in the form of an axially extending conductor, embedded in the rotor shaft, which finally continues as a second radially outwardly-directed conductor portion which is connected to a point in that part of the rotor winding which is surrounded by a winding capsule. When the rotor speed increases from zero to its maximum value, the diameter of the winding capsule will increase considerably, for example by 5 mm, under the influence of centrifugal forces, and it may be assumed that the above-mentioned second radial conductor portion, similar to corresponding conductor portions of other known rotors, is connected to the rotor winding via a flexible conductor element. This flexible element is also stressed by movements of a relatively small amplitude but of a high frequency, namely movements substantially caused by deflection of said first shaft portion, i.e., in the shaft portion which is not connected to the driving turbine.
It has proved to be very difficult to achieve a sufficiently reliable, flexible connection between the rotor winding and the current feeding system of the rotor winding, and it has often been found that fatigue breakdown has taken place in the above-mentioned flexible conductor element after some time in operation. In the case where the fatigue failure is a complete breakage of the flexible conductor element, an arc arises which can easily result in harmful heating of the winding capsule, which in turn may cause very serious damage.
There have also been examples where the provision of radial conductor channels in the rotor shaft have resulted in shaft fracture.
In addition to the drawbacks mentioned above, the machine has the disadvantage that the current conducting means used for supplying current to the rotor winding is inconvenient and unreliable due to the fact that it comprises axial conductor units and radial conductor units, which have to be arranged in corresponding channels in the rotor body before they can be connected to each other.
With the rotor described in specification No. 3,493,795, the last-mentioned drawback is avoided since a shaft portion extending from the active portion of the rotor body is provided with two straight, mutually diverging conductor channels, each channel containing a single feeding conductor unit only. However, the channels terminate at the surface of the rotor shaft at an axial distance from the active portion of the rotor body. From the openings of the channels radially extending parts of the feeding conductors are connected to coil end portions extending axially from the active portion of the rotor body. The radially extending parts of the feeding conductors are subjected to fatigue failure - at least to the same extent as the above-mentioned flexible conductor elements. Further, the channel openings constitute indications of fraction, and since they are located at the surface of a relatively thin portion of the rotor body, they may result in shaft fracture.